Roasting of zinc sulphide ores



Patented 1m 14, 1932 PATENT OFFICE STANLEY ROIBSON, OF AVONMOUTH, ENGLAND ROASTING 0F ZINC SULPHIDE ORES Ho Drawing. Application filed September 20,

Various processes have been proposed and operated for roasting zinc sulphide ores, concentrates and the like for the production of a sinter or porous material suitable for subsee uent distillation for the recovery of the zinc.

0st of these processes involve two operations the first of which is carried out in ordinary roasting furnaces of various types and is intended to reduce the sulphur content of lo the ore or concentrate in some cases to about 8 to 10%, and in other cases to less than this amount. Still other proposals have been made to dead-roast the ore, i. e. to eliminate the sulphur as completely as is possible in the first roasting operation, and then to add a proportion of green or unroasted ore or carbon. The material then underwent a second operation consisting of a blast roast in which air was forced or induced through an a bed of the material on a travelling grate, the product being a desulphurized sinter of porous coke-like character. 7

lhe operation of these processes presents certain difliculties. In the first place it is desirable that the sulphur-bearing gases evolved during the process should be capable of use commercially for the manufacture of sulphuric acid. In the two-stage processes the gases from the first operation may be sufficiently rich in sulphur for this purpose. The gases from the blast roasting, however, are too poor in sulphur and either they must be enriched in some way, for instance as in one prior proposal by passing them over the ore undergoing the preliminary roast, or they must be exhausted to the atmosphere which is the usual procedure.

Owing to the tendency of the legislatures .of the various industrial countries to prohibit the roasting of ores under such conditions that the sulphur dioxide produced is sent without further treatment to the atmosphere, considerable. -limitation has been placed on the operation ofsintering or blast roasting, and it is an essential condition for the wide extension of this process in such countries that the gases evolved be utilized in a subsequent manufacture or in other ways prevented from contaminating the atmosphere.

1928, Serial No. 307,338, and in Great Britain October 24, 1927.

A further difliculty in the two-stage process is that of dead-roasting the ore in the first stage.

Now the primary object of the present invention is to eliminate the necessity for preroasting or dead-roasting zinc sulphide ores or concentrates on a separate roasting furnace prior to the blast roasting operation, and further so to conduct the blast roasting operation that a gas can be produced which is sufiiciently rich in sulphur without further treatment for the purpose of sulphuric acid manufacture. The conditions necessary to realize this object are that the bed of material undergoing the blast roast be sufliciently porous to allow air to be drawn readily therethrough without excessive suction and that atmospheric air other than that drawn through the bed of material should be ex,- cluded from the apparatus.

The present invention is a process for the production from zinc sulphide ores, concentrates and the like of a porous material suitable for subsequent distillation for the recovery of the zinc, consisting in mixing with the green ore concentrate orthe like a coarse granular or nodular material in proportions sufiicient to ensure such porosity in the mixture that air can be readily drawn therethrough, and then subjecting the mixture to blast roasting in a single operation and with substantial exclusion of air except through the charge itself so as to obtain both a sintered or nodulized product and a gas sufficiently rich in sulphur without further treatment to enable it to be used for the manufacture of sulphuric acid.

I have found it most convenient to use for each batch of raw material some of the already roasted product from a preceding blast roast. It may here be stated that the product of my improved process is in the form of porous grains or nodules which tend to retain their formation whenlumps of the product are crushed, whereas the sinter from previously proposed processes tends to pulverize under this treatment. It is very largely due to this relatively coarse granular state of the admixed material that the desired porosity of the charge is obtained. It may even be desirable to screen the crushed sinter before mixing it with a fresh batch of ore so as to obtain a large proportion of these porous nodules of onesixteenth to one-eighth inch diameter. 0

A fairly large quantity of a previously roasted product should be used in order to obtain the desired porosity in the mass. For instance with the well-known Australian zinc concentrates containing from 27% to 30% sulphur, I have found that about at to 5 parts of the previously roasted product to one part of the unroasted concentrates gives Nery satisfactory results the total sulphur content of the mixture prior to blast-roasting being in the region of 4% to 7%. The added particles besides opening up the bed of ore to allow the free passage of air seem to act as nuclei for the formation of porous nodules of zinc oxide. The high porosity of the mass undergoing roasting permits a limitation of the draught such that almost all of the gases produced can be utilized for sulphuric acid manufacture. T he remainder of the gas is of such dilution that it can be passed direct to the atmosphere.

To make the most effective use of the present invention from the standpoint of utilizing the sulphurous gases, modifications should be made in the existing types of blast roasting or sintering machines with the object of preventing the admission of air other than through the bed of ore itself.

I am aware that a process of roasting zinc sulphide ores has recently been proposed in which the sulphur of the sulphide ore is reduced by mixing raw ore with sulphide ore which has already been subjected to a sintering operation in a sintering blast apparatus, the mixture thus obtained being treated direct in a roasting blast apparatus with a view to its complete desulphurization and subsequent reduction.

I make no claim to such a process per se. In the process of my present invention the addition of already sintered material is utilized to increase the porosity of the charge as well as to reduce the sulphur content thereof. It is not essential however to use sintered zinc oxide as the added material. I prefer to use it because it is readily available, and because it does not lower the zinc content of the final product. Crushed pumice or granular volatilized or precipitated zinc oxide in an agglomerated form, or granular zinc retort residues or crushed slags from lead blast furnaces or mixures of these materials or indeed any other inert diluent material in a suitably coarse granular state may be used.

\Vhat is essential, however, for the purpose of the present invention is that the blastroasting operation be so conducted with substantial exclusion of air other than that drawn through the charge itself that the resulting gas is available, without further treatment as regards its sulphur content, for the manufacture of sulphuric acid.

What I claim is l. A process for the production from zinc sulphide ores, concentrates and the like of a porous material suitable for subsequent distillation for the recovery of the zinc, consisting in evenly mixing with the green ore, concentrate or the like agranular material containing a major proportion of particles of one-sixteenth to one-eighth inch granular size and in such quantity that the mixture has a sulphide sulphur content of four to seven percent and blast-roasting the mixture in a single operation.

2. A process for the production from zinc sulphide ores, concentrates and the like, of a porous material suitable for subsequent distillation for the recovery of the zinc, consisting in evenly mixing with the green ore, concentrate or the like disintegrated sintered material from a preceding blast roasting operation, in quantity sufficient to reduce the sulphide sulphur content of the mixture to from four to seven percent, the returned sinter containing a major proportion of particles of from one-sixteenth to one-eighth inch granular size, and blast-roasting the mixture in a single operation.

8. A process for the production from zinc sulphide ores, concentrates and the like of a porous material suitable for subsequent distillation for the recovery of the zinc, consisting in evenly mixing with the green ore, concentrate or the like a granular material containing a major proportion of particles of" from one-sixteenth to one-eighth inch granular size and in such quantity that the sulphide sulphur content of the mixture is from four to seven percent, blast-roasting the mixture in a single operation with substantial exclusion of air other than that drawn through the charge itself and obtaining both a porous desulphurized product and a gas sufficiently rich in sulphur Without further treatment to enable it to be used for the manufacture of sulphuric acid.

4. A process for the production from zinc sulphide ores, concentrates and the like of a porous material suitable for subsequent distillation for the recovery of the zinc, consisting in evenly mixing with the green ore, concentrate or the like, a granular material containing a major proportion of particles of from one-sixteenth to one-eighth inch granular size and in such quantity that the sulphide sulphur content of the mixture is from four to seven percent, and blast-roasting the charge under induced draught with substantial exclusion of air other than that drawn through the charge itself.

5. A process for the production from zinc sulphide ores, concentrates and the like of a porous material suitable for subsequent distillation for the recovery of zinc, consisting.

in evenly mixing with the green ore, concentrate or the like disintegrated sintered material containing a major proportion of particles of from one-sixteenth to one-eighth 6 inch granular size and in such quantity that the sulphide sulphur content of the mixture is from four to seven percent, blast-roasting the mixture in a single operation With substantial exclusion of air other than that 10 drawn through the charge itself and obtaining both a porous desulphurized' product and a gas sufiiciently rich in sulphur without further treatment to enable it to be used for the manufacture of sulphuric acid. STANLEY ROBSON.

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